High quality audio amplifier systems have for many years operated with multi-band amplifier configurations. One of the primary reasons for this was that it is difficult to design a single loudspeaker that can adequately cover the entire audio band. Therefore, a different speaker may be used to cover each portion of the audio spectrum. However, other benefits are obtained such as more headroom from the system with smaller wattage power amplifiers for the overall same output than could be obtained from a single large power amplifier. These types of systems sound cleaner at higher power levels because bands of frequencies are isolated from each other in each channel of amplification, resulting in decreased inter-modulation distortions.
Test and measurement instruments suffer similar problems with wideband input signals. For example, in an oscilloscope, one of the difficult aspects of making a wideband pre-amplifier is the need for an attenuator between it and the input signal. The wider the bandwidth, the more difficult it is to maintain good return loss at the input to the scope. As a result, a 50 ohm match is generally not achieved over the desired bandwidth, degrading the quality of the signal.
Accordingly, a need remains for an improved multi-band amplifier for use in test and measurement instruments.